1. Field of the Invention
The present invention is directed to the field of planar magnetic transducers and, more particularly, to the treatment of diaphragms and conductor circuits associated with diaphragms which are mounted in spaced proximity to permanent magnets mounted to support frames forming the transducers. More specifically, the invention is directed to physically deforming the diaphragms and/or conductor circuits applied thereto when in a non-tensioned state and thereafter stretching the diaphragms and conductor circuits to place them under tension within a support frame. When mounted, the diaphragms are relatively flat but contain creases or ridge lines which allow limited flexing of the diaphragms and/or conductor circuits for purposes of maintaining diaphragm tension and reducing distortion of the diaphragms during use and to compensate for temperature variances created by the passage of electricity through the conductors during use of the transducers.
2. History of the Related Art
Planar magnetic transducers or speakers conventionally utilize flat metallic foils or wires to create conductor runs on the surface of a diaphragm which is mounted within a support frame and held under tension generally in a plane parallel to the pole faces of one or more permanent magnets. The path for the electrical conductor runs on a diagram is generally chosen so the current flowing through the conductor induces net magnetic forces of uniform direction for all of the conductor segments or runs within what is referenced as an "active area" or "active surface area" of the diaphragm, thereby causing the general direction of diaphragm motion to be perpendicular to the diaphragm surface during operation of the transducer. The "active area" or "active surface area" of the diaphragm, and as described and referenced throughout this application, both in the specification and claims, is that area of the diaphragm which is not constrained from motion by a rigid frame which supports the diaphragm relative to the one or more permanent magnets.
The conductor runs applied to a diaphragm result in resonance modes which cause the diaphragm to exhibit modal behavior patterns at certain frequencies throughout the operating range of the transducer when power is applied to the electrical conductor circuits from a conventional amplifier. During the use of smaller planar magnetic transducers, as power levels increase beyond approximately one watt per square inch, heat builds up along the metal conductor runs or segments. The conductors are typically an aluminum material which expands at a much greater rate than the substrate of the diaphragm which may be a synthetic plastic or film, such as Mylar.TM.. The heat causes the two materials to expand at different rates resulting in a loss of tension or non-uniform tension over parts of the "active area" or "active surface area" of the diaphragm. In large planar magnetic loudspeakers with diaphragms in excess of 100 square inches, the surface area of the diaphragm limits the temperature buildup and diaphragms exhibit relatively normal behavior when electrical energy is applied to the conductor circuits. However, with small planar magnetic transducers used as loudspeakers, the heat buildup is greater for a given amount of input power because of the reduced surface area of the diaphragm associated therewith.
The loss of tension across a diaphragm results in non-uniform displacement of the diaphragm during operation. Such non-uniform displacement of the diaphragm in turn causes several forms of distortion limiting maximum usable sound output. The non-uniform displacement also causes a non-piston-like behavior of the diaphragm creating valleys and peaks in the frequency response of the loudspeaker, thus resulting in non-linear sound output levels at varying frequencies. The non-uniform displacement also creates a doubling or buzzing type of distortion where multiple harmonics may be generated at the diaphragm. In such instances, the diaphragm moves at two different directions at the same time. This movement behavior takes the form of pockets of the diaphragm moving in opposite directions which results in a change of output when different frequencies are applied to the loudspeaker. As the input frequency is changed, various patterns emerge from the diaphragm due to the velocity of the waves traveling along the diaphragm. Ideally, the behavior of the diaphragm is like a piston throughout the normal frequency operating range.
It should be noted that ribbon loudspeakers, ribbon tweeters and planar ribbon loudspeakers utilize diaphragms which are not tensioned and are usually loosely suspended. Such loudspeakers have made use of corrugated aluminum diaphragms but not for purposes of reducing loss of tension across a diaphragm or for compensating or offsetting for heat buildup of conductors extending across a diaphragm.